Pest specialists find spotted wing drosophila problematic in state

Dec 17, 2012

University of Maine Cooperative Extension pest management specialists tracking the invasion of the crop-damaging spotted wing drosophila fruit fly in Maine report that trapping results and surveys indicate that the pest has already become established and problematic in most of the state.

UMaine Extension experts David Handley, a vegetable and small fruit specialist at Highmoor Farm in Monmouth, and James Dill, a pest management specialist in Orono, have been setting and checking flytraps statewide to catch the fruit flies and assess their incidence. They also are analyzing survey data from farmers who are assisting with the assessment.

"We were still catching high numbers of fruit flies into November, but the numbers have dropped pretty steeply over the past two weeks, probably due to the colder temperatures and lack of food," says Handley. "Any farm we set a trap at, we caught these flies, often in very high numbers—thousands—which is pretty impressive when you consider that they first arrived in Maine last fall."

Handley and Dill had traps set up at berry farms from Wells to Orono, and Frank Drummond, professor of entomology at the University of Maine, had numerous traps in wild blueberry fields in the Down East region.

Most fruit and berry growers noticed fruit flies on their crops, especially later in the summer, but most did not see high levels of damage from the larvae if they controlled the adults. Where the adults were not controlled, most of the late season fruit contained larvae, causing it to rot prematurely.

The spotted wing drosophila originated in Asia and traveled in fruit and vegetable imports to California. In the past three years, the invasive pest has spread up and down both coasts and into the Midwest. The small flies resemble common fruit flies except for a saw-like appendage on the female's ovipositor used to bore into the soft skin of fruits like blueberries and raspberries to lay eggs. The white larvae feed on the fruit from the inside, destroying it in the process. Common fruit flies must wait until fruit gets overripe before they can lay eggs in it.

Maine growers and agricultural scientists fear the invasion of the spotted wing drosophila could devastate soft fruit crops, particularly if growers are trying to avoid chemical pesticides to control insects. So far, frequent applications of pesticides appear to be the only effective way to control the tiny flies, according to Dill.

"The good news is that we have pesticides that will control them pretty well, including some materials that are available for organic farmers," he says. "The bad news is that frequent applications are needed because of the vast numbers of flies that are continually invading the crop."

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